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8 & 10 cyl Bristol cars Type 407 onwards - restoration, repair, maintenance etc

How do I remove gauges/instruments in 408 and ammeter v voltmeter ?

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Old 29-01-21, 01:34 PM
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Default How do I remove gauges/instruments in 408 and ammeter v voltmeter ?

My 408 has an aftermarket temperature gauge that looks too different from the original, a non-functioning clock, and ammeter whose needle bounces all the time and the fuel gauge does not work (that could be either the wiring or sender - I haven't investigated yet).

Anyway, some of these gauges are going to have to come out for repair or replacement. So how do I do that? I see one of Stefano's 409 restoration photos shows the shroud around the instrument panel and steering column removed as one piece http://www.stefanopasini.it/images/B...Dismantled.jpg.

So do I have to take off the steering wheel to get access to the rear of the instruments? If I get that shroud off, can I change the gauges without removing the wooden instrument panel completely.

Also, does anybody have an opinion on mechanical versus electrical gauges for water temperature and on replacing the ammeter with a voltmeter?

thanks

David
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Old 29-01-21, 05:48 PM
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Default CAI

I do not think you need take off the steering wheel, though it might make access easier. I would be tempted to update to a voltmeter.

For information - Caerbont Automotive Instruments Ltd (CAI) is an independent company in South Wales who have their roots in the Smiths Motor Accessories business. In 1984 ownership moved to the Lucas Group and then to VDO before becoming independent following a management buyout in 1993. CAI was the subject of a second MBO ten years ago.

They have the majority of the original Smiths tooling and should be able to repair or replace most of the instruments. They have also bought up Speedy Cables. I have a full suite of 411 instruments on order from them - they are prepared to make bespoke ones if they have the pattern. For example I want the fuel filler symbol (words would be disproportionately expensive) to point to the side of the filler cap as most modern cars do.

Their email is at info@caigauge.com

Brian
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Old 29-01-21, 07:35 PM
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Quote:
Originally Posted by Xseries View Post
I do not think you need take off the steering wheel, though it might make access easier. I would be tempted to update to a voltmeter.

For information - Caerbont Automotive Instruments Ltd (CAI) is an independent company in South Wales who have their roots in the Smiths Motor Accessories business.
>
>

Brian
Thanks, Brian.

David
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Old 30-01-21, 06:17 AM
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Default How do I remove gauges/instruments in 408 and ammeter v voltmeter?

David,

It's best to remove the steering wheel first. The binnacle has two screws on top and lower down. Once the binnacle is off, the instrument panel can be moved forward. Each instrument must have both the lighting wiring and the information sender wiring removed. There is a metal bracket held on with two knurled knobs that screw on to studs attached to the rear of each instrument. Undo these and remove the bracket and the unstrument will come free.

John K.
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Old 30-01-21, 02:19 PM
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You definitely have to remove the steering wheel in order to remove the binnacle, but before you do anything disconnect the battery and make sure that the steering wheel is in the straight ahead position. The horn push simply pulls out and once you have loosened the steering wheel clamp using a c spanner you will find that it is still retained by a simple c clip which needs prizing out. As John Keighley says the binnacle is held in place with two screws at the top and two at the bottom but NB they may be different lengths. The binnacle can be quite a tight fit and may need a little gentle persuasion to get off.

Once the binnacle is off I recommend that you remove the four screws that hold the instrument panel in place so that you can angle it forward to improve your access. You may need to remove the speedo drive.

If you are going to remove more than one instrument at a time donít rely on your memory as to which wires go where and label all the wires you remove

Coming to the instruments themselves

The ammeter is of course wired as an ammeter and (almost) all the current to and from the battery passes through it. Replacing it with a voltmeter is not that straightforward as you have to maintain the circuit that it is in. Also bear in mind that a voltmeter will only tell you that something has gone wrong sometime after the battery has started to die. Iíd suggest that if the ammeter is jiggling all the time itís actually doing its job and is flagging up a problem in somewhere between the dynamo and the battery which of course also includes the return path via the vehicle and engine earth paths. This might be down to the connections on the back of the ammeter itself needing to be tightened but an ammeter is a very simple device and there is pretty much nothing that can go wrong with the internals.

The petrol gauge will, contary to what you might expect, show full, full, full all the time if the sender in the tank or indeed the wiring to the tank is open circuit. So thatís unlikely to be a problem at the tank end. I havenít experienced your problem of showing empty all the time but Iíd suspect one of two possibilities, either the supply to the gauge has failed or the earth on the gauge has failed. Once again the gauge itself is a fairly simple device - I found the best explanation of how it works on, of all places, an Austin 7 website. Essentially as I recall two electromagnets work against each other to operate the needle, which requires power from the battery to the gauge AND an earth on the gauge.

Which brings me to the next point, this sort of petrol gauge and indeed the mechanical temperature and oil pressure gauges do not need a voltage stabiliser, so there isnít one. Which is a further complication to replacing the temperature gauge with an electrical gauge.

The clock originally relied on an electrical contact pulsed by the balance wheel which over time will have tarnished and pitted to the point where there is no contact and everything stops. As far as I know there is no clock that is the right size in anybodies catalogue any longer. I think there was an article in a fairly recent BOC Bulletin describing a modification kit that is available that substitutes an optical interrupter for the said contact, which, coupled with some clever electrical circuitry archives the same effect. Iíll try to find time to look it out.

While you have access to the back of the instrument panel Iíd counsel replacing the extremely dim and inadequate instrument bulbs with LEDs. Why anybody ever needed a dimmer rheostat on those original bulbs is a mystery to me but the good news is that the existing dimmer rheostat will still dim the instrument lighting if you leave the old incandescent bulbs in the lighting over the central heating controls and switches. I used https://www.bettercarlighting.co.uk/index.php? Itís also well worth putting an led in the interior light.

Presumably you are happy with the accuracy of the Speedo and the Rev Counter. But it is worth knowing that the Rev counter can get to read much higher than actual rpm over time. If you need to know more please come back to me

Roger
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Old 30-01-21, 02:31 PM
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Quote:
Originally Posted by John Keighley View Post
David,

It's best to remove the steering wheel first. The binnacle has two screws on top and lower down. Once the binnacle is off, the instrument panel can be moved forward. Each instrument must have both the lighting wiring and the information sender wiring removed. There is a metal bracket held on with two knurled knobs that screw on to studs attached to the rear of each instrument. Undo these and remove the bracket and the unstrument will come free.

John K.
Thanks, John
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Old 30-01-21, 03:15 PM
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Very interested in the advice given which I am sure is very accurate. I recently did a lot of work in this area on my 411 and 412. My approach was to undo the 2 screws that hold the timber panel in place and prize the timber panel forward. The only problem I had doing this is that you would need to undo the speedo cable from the back of the speedo once you get things moving to enable the timber to move forward far enough to enable good access to the back of the gauges.

The fuel gauge in my 412 sat on empty. Replacing the tank sender solved the problem.

The 412 had an aftermarket amp meter when it should have had a volt meter. This required my auto electrician to correct the wiring.

Best of luck
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Old 31-01-21, 02:07 PM
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Quote:
Originally Posted by PEU186F View Post
Presumably you are happy with the accuracy of the Speedo and the Rev Counter. But it is worth knowing that the Rev counter can get to read much higher than actual rpm over time. If you need to know more please come back to me

Roger
Thanks for the detailed advice, Roger. As to the larger gauges, I haven't checked them yet for accuracy. I will before I start on the project to get all the gauges functional, accurate and aesthetically matching.

David
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Old 02-02-21, 10:41 AM
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Quote:
Originally Posted by peter dowdle View Post

The fuel gauge in my 412 sat on empty. Replacing the tank sender solved the problem.
Peter, et al

The 411 wiring diagrams on this site show that there was a step change in wiring and fusing practises after the 410, fusing in particular was vastly improved. They also show that the fuel and temperature gauges were fed by the voltage stabiliser which is required by the gauges that incorporated a heated bimetallic strip, that were the standard by this time. These will show empty if the tank sender or wiring fails to open circuit. This type of gauge characteristically takes a little time to react when you turn the ignition on but does have the advantage that it doesnít waver about as the fuel sloshes about in the tank.

The gauge used in the 410 and earlier cars , which relies on opposing electromagnets, doesnít require voltage regulation, does react instantly when one turns the ignition on and does waver about as the fuel moves about and also fails to (beyond) full if the tank sender or its wiring go open circuit.

Note that the tank senders have to have different characteristics to operate the two different types of gauge correctly, one shouldnít change one without changing the other.

I trust this clarification may be a help to somebody someday

Roger
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